The present invention generally relates to magnetic flux concentrators and methods of manufacturing magnetic flux concentrators.
Magnetic flux concentrators, sometimes referred to as flux guides, flux focusers, flux intensifiers, flux diverters, flux controllers, flux reflectors and other names, are generally known and have been used in inductive heating and inductive power transfer applications. Flux concentrators intensify the magnetic field in certain areas and can assist in increasing efficiency in power or heat transfer. Without a concentrator, the magnetic field is more likely to spread around and intersect with any electrically conductive surroundings. In some circumstances, a magnetic flux shield can be a type of magnetic flux concentrator.
Soft magnetic materials, that is materials that are magnetized when an external magnetic field is applied, are sometimes used in manufacturing flux concentrators. Soft magnetic materials have magnetic domains that are randomly arranged. The magnetic domains can be temporarily arranged by applying an external magnetic field.
One of the most common soft magnetic materials used in manufacturing flux concentrators is ferrite. Ferrite flux concentrators are dense structures typically made by mixing iron oxide with oxides or carbonates of one or more metals such as nickel, zinc, or manganese. The variety of “ferrites” is extremely diverse, because of the numerous combinations of metal oxides, including some that contain no iron. Typically, they are pressed, then sintered in a kiln at high temperature and machined to suit the coil geometry. Ferrites generally have very high magnetic permeability (typically over μr=2000) and low saturation flux density (typically between 3000 to 4000 Gauss). The main drawbacks of ferrite flux concentrators are that they are often brittle and tend to warp when manufactured in thin cross sections. Ferrites also typically have a low saturation flux density and therefore become saturated easily and thus are no longer significantly more permeable to magnetic fields than air in the presence of other magnetic fields, which may be undesirable in some applications. Ferrite flux concentrators are sometimes made thicker to compensate for the brittleness and poor saturation flux density. Ferrite flux concentrators may be machined thinner, though the hardness can make it difficult. However, machining thin components will not resolve the saturation issues or volume manufacturability. Further, machining components can make mass production expensive and difficult.
Another soft magnetic material sometimes used in manufacturing flux concentrators is magnetodielectric materials (MDM). These materials are made from soft magnetic material and dielectric material, which serves as a binder and electric insulator of the particles. MDM flux concentrators come in two forms: formable and solid. Formable MDM is putty-like and is intended to be molded to fit the geometry of the coil. Solid MDM is produced by pressing a metal powder and a binder with subsequent thermal treatment. The characteristics of an MDM flux concentrator vary based on, among other things, binder percentage. Typically, the less binder the higher the permeability. However, in conventional arrangements, less binder translates to more metal on metal contact, and therefore more eddy currents forming during use of the flux concentrator. Although MDM flux concentrators may be manufactured with a thin profile, it is difficult to manufacture an MDM flux concentrator with all of the desired magnetic and thermal characteristics due to the competing effects of varying the binder percentage.
Consumer electronics, such as cell phones, mp3 players, and PDA's, are trending toward slimmer profiles. Simultaneously, there is increasing demand for portable devices to be capable of receiving wireless power. Current flux concentrators suitable for use with wireless charging systems are generally too thick and therefore can noticeably increase the profile of consumer devices. Accordingly, there is a desire for a method of manufacturing a thin flux concentrator that has the desired magnetic and thermal characteristics suitable for use with a wireless power transfer system.